Additive layer manufacturing (ALM), selective laser sintering (SLS) and solid freeform fabrication (SFF) techniques, generally termed as 3D printing techniques, may be used in procedures for building up three-dimensional solid objects based on digital model data. Such 3D printing employs an additive process where layers of material are sequentially built up in different shapes. The 3D printing is currently used for prototyping and distributed manufacturing with multiple applications in engineering, construction, industrial design, automotive industries and aerospace industries. For example, document DE 10 2009 034 566 A1 discloses a method for manufacturing a fuel tank employing a generative layer manufacturing procedure.
Such 3D printing systems usually employ a combination of a computer-aided design (CAD) system and an operational 3D printing tool that performs the layer manufacturing on the basis of a manufacturing model generated by the CAD system. A three-dimensional CAD digital representation of the component to be manufactured is subjected to a so-called “slicing” procedure where the digital model is sliced up into layers of a predetermined thickness with the orientation of the layers being perpendicular to the printing direction of the 3D printing tool. A common layering procedure involves building up a tessellated surface model. Such models are built by intersecting sets of horizontal planes with the three-dimensional CAD digital representation, resulting in a multitude of closed curves or polygons. The space between any two consecutive horizontal planes is referred to as a “slice”.
The layer model may for example be described in stereolithography (STL) format which only describes the surface geometry of a three-dimensional object as raw unstructured triangulated surface using a three-dimensional Cartesian coordinate system. The 3D printing tool is capable of reading and interpreting STL models in order to generate each layer of the component to be printed using one of several specific physical fabrication processes, such as selective laser sintering (SLS) or Fused Deposition Modeling (FDM).
When building up a component layer by layer according to a digitalized layer model, most regions of a layer under construction are self-supported, i.e. the layer under construction is built up directly on top of the previously built-up layer. However, there may be regions of a layer under construction that extend sideways, i.e. perpendicular to the printing direction of the printing tool, beyond the planar extension of the previously built-up layer. Forming a tangent between the outermost point of a previously built-up layer and the outermost point of the layer under construction will yield an overhang angle between the axis normal to the plane of extension of the layers and the resulting tangent.
Regions with steep walls, i.e. with a low overhang angle, tend to be completely self supporting. Parts with shallower walls, i.e. with a high overhang angle, will exhibit problems during the built-up process since the upper layer will not be sufficiently be supported by the existing lower layers. Depending on the type and characteristics of the manufacturing material and the printing conditions, such as manufacturing speed, temperature or layer thickness, the threshold for the overhang angle beyond which a layer under construction will not be sufficiently supported by the lower layers any more will vary.
A conventional measure for allowing the formation of overhang structures with overhang angles above the threshold is to provide additional supporting structures or elements along the shallower walls.
As alternative, document DE 10 2012 008 371 A1 discloses a method for manufacturing a component having an overhang which comprises iteratively carrying out the process steps of applying a layer section with predetermined dimensions of a particulate material in a predetermined region on a base layer, and heating the layer section by means of a heat source in such a manner that the particles of the material within predetermined dimensions bond. A local buildup angle occurring between two consecutive layer sections of an overhang is not allowed to exceed a predetermined maximum buildup angle to a perpendicular of the base layer.